Field
The presently disclosed subject matter elates to methods and systems for distributed control of an industrial process. More particularly, the presently disclosed subject matter relates to a modular interoperable distributed control system.
Description of Related Art
Distributed control systems (DCS) are used for the control of industrial processes. In contrast to centralized control systems, distributed control systems include a plurality of control nodes distributed throughout the system. The first generation of DCSs (1970s to mid-1990s) consisted of mostly single supplier proprietary controllers, operator stations and engineering consoles connected to a shared network/bus. These early DCSs were designed to replace panel mounted single loop electric or pneumatic controllers. The DCS controllers handled a small number of control loops and I/O (typically between 8 to 50) requiring the development of complex redundancy schemes given that the scope of failure of a single DCS controller was significantly higher than that of a single loop controller. Depending on the DCS, the end user could connect a proprietary vendor supplied application computer or another supplier's general purpose computer only if the DCS supplier provided an interface for it.
The 2nd generation of DCSs (late 1990s to present) consisted of the same basic architecture with the replacement of some previously proprietary components by commercially available Ethernet switches connecting general purpose servers and workstations (usually running the Microsoft Windows operating system). These systems, however, still used a vendor supplied proprietary controller communicating through a proprietary application layer protocol running over the Internet Protocol (IP). More recent 2nd generation controllers can handle hundreds of control loops in a single controller.
In both the 1st and 2nd generation DCS systems, however, all I/O is physically bound to a single controller, limiting the usage of that I/O to only one single controller. In the current hierarchical DCS model, each I/O network is subordinate to a single controller. Once a controller is fully loaded, a project that adds a single field device must fund an entirely new redundant controller along with ancillary equipment and associated engineering. This can result in lost opportunity if the project is cancelled (because the rate-of-return falls below the cost of capital) or lowering return on capital employed if the capital is spent inefficiently.
Moreover, in the existing DCS market space, systems can lack interoperability because the end user lacks the freedom to incorporate any innovation directly into the DCS that does not come from the DCS supplier. This restriction can arise from the use of supplier proprietary application protocols which only allow devices and software from the supplier to be used by the DCS. Current control system architectures can: (1) lock the buyer into the hardware components available from a single vendor at a single point in time with limited opportunity to mix-and-match the best-of-breed, and (2) block an economically feasible path to upgrade as new and better components emerge in the marketplace. Encouraging a supplier to extend the life of aging and obsolete control system infrastructure does not necessarily create a differentiated competitive advantage (e.g. customers of the same supplier can also benefit from the same life extension). Furthermore, if one single customer jointly develops and funds the life extension R&D, it may serve as a competitive disadvantage to that customer. Today's DCS architectures can require periodic wholesale DCS replacement projects to move between generations of supplier technology. These replacement projects are expensive, lengthy and disruptive to ongoing operations.
Furthermore, many integrated petrochemical companies operate manufacturing facilities ranging from small polymer extrusion lines to world class, integrated refining and chemical complexes, yet use essentially the same DCS developed for the largest installation in those facilities. Older manufacturing facilities without access to advantaged feedstocks will be challenged to remain competitive as new capacity comes online that exploits economies of scale, integrates modern energy efficient process & equipment technologies, aligns conversion capacity with forecast market demand and integrates state-of-the-art automation technology
Profit-enabling application software is often delivered on the operations management level (ISA95 level 3) where the network and computing appliances are open and accessible to any third party software developer. The benefits realized from applications built on today's closed, proprietary systems can thus be limited to the resources and capabilities of the supplier and buyer. In addition, closed, proprietary architectures can diminish the incentive for third party software development and therefore a buyer's access to best-of-breed technology through an open applications marketplace.
Accordingly, there is a desire for a DCS that can economically scale in any direction, small or large, and that can flexibly incorporate innovative applications faster across disparate manufacturing lines, in accordance with an exemplary and non-limiting embodiment, a modular, interoperable DCS architecture can include of two types of Distributed Control Nodes (DCNs); Application DCNs and Device DCNs connected to a high speed Layer 3 Ethernet switch fabric using the IP protocol. An industry standard service/software runtime called the “DCN Service” is resident on all DCNs providing all control application level communication and FBD execution services.